Project 3: Translational Model of Cell-Based Therapy for Myocardial Infarction. Project 3 proposes to develop and test in vivo, cell-based therapies to improve cardiac function following infarction. Two therapeutic approaches will be studied: 1) Injection of immortalized, clonal populations of marrow stromal cells (MSC), or their secreted products, to facilitate endogenous recovery. 2) Engraftment of exogenous cardiomyocytes (CMs), with/without MSC or MSC-derived factors. The exogenous CMs will be harvested from prenatal hearts or differentiated from either embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC). These studies will be performed first in a rat model, which is well developed by investigators in this program, and allows for a sufficiently large number of animals to test several variables. Once a beneficial protocol is identified in the rat model it will be applied to the canine model. Torok-Storb and colleagues have extensive experience with cell transplantation in the dog model. In particular the issues of allograft rejection and the benefits and consequences of immunosuppression accurately reflect these same complications in patients, therefore strategies to address these issues will be clinically relevant. This stepwise plan, from rats to dogs, will limit the number of dogs required. There are three specific aims to address these goals. Aim 1 proposes to generate and characterize cardiomyocytes (CM) derived from canine embryonic stem cells (ESC) and from induced pluripotent stem cells (iPSC). Aim 2 will test the hypothesis that MSC facilitate endogenous repair and revascularization, induce tolerance, and promote engraftment of cardiomyocytes in the rat model. For this purpose immortalized and cloned MSC lines have been generated to provide reagents that can be well characterized and provide a consistent product for investigation. Dog MSC lines functionally analogous to rat MSC lines will be identified and used in Aim 3 to repair an infarcted heart in the dog model. These studies will serve to establish a robust large animal model for developing protocols and testing the efficacy and safety of cell based therapies for treating myocardial infarcts.